Fair price for a year-old B100R (buying from a friend)

I just heard from a co-worker that his daughter had a bass and amp for sale...he called me to tell me what kind it was, and I was surprised that it was a B100R. Although I have yet to go play it, my friend says his daughter rarely ever played either the bass (an Ibanez SR205(?) or used the amp. In looking online, they go new for $550...being a pretty decent guy, I want to make it right - for me, AND for her. I know this is a big hypothetical, but what would some of you that have played them say would be a fair price for a supposedly almost new amp? My main cab is a 21012 Schroeder, and between that and my rack, I'm looking at 125 lbs and would love something lighter, and from what I've read the reviews are almost universally positive.